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It's tough to believe, but in-car GPS navigation has already been around for more than a decade. Yet were it not for politics—and Einstein's theory of relativity—we wouldn't even have it in the first place.

Twenty years ago, a road trip meant a bunch of fold-out maps stuffed into your glove box or your car door panel pockets. Pulling over, unfolding one like a giant newspaper, and then figuring out where you were and how it corresponded to what you were seeing through the windshield was the norm. Along the way, those maps gave way to MapQuest or Yahoo Maps print-outs, and now, fortunately, we've got portable navigation devices (PNDs), in-dash GPS systems, and GPS-enabled smartphones. Voice-enabled navigation is more commonplace than ever, as the average PND price keeps getting lower and lower, and high-quality navigation apps are available for most smartphones. Android phones even come with free Google Maps with driving directions.

But to figure out how we got here, we need to first look at how it all began.

Einstein and the Origins of GPSThe U.S. Department of Defense first developed satellite-based global positioning technology for the military. An early satellite-based system dubbed TRANSIT was up and running as early as 1960, with more refined and precise versions involving multiple satellites in general military use by the early 1980s (pictured, right). But it wasn't until 2000 that precision GPS navigation became open to the public.

Publicly available GPS devices had already been around since the early 1980s. But the military added interference to the signals to ensure their own version was the only one that could be used with any precision. After four years of deliberations, President Clinton signed a bill in 2000 ordering the military to cease scrambling satellite signals used by civilians. This instantly upgraded the accuracy of the few consumer-based systems already in existence by a factor of 10, and opened the doors to a much larger, consumer electronics-based industry for GPS navigation.

Today, a network of 24 U.S.-based GPS satellites orbit the earth, ensuring that at least three are available at any one time for a device's position request anywhere on the globe. Russia's own GLONASS system of 22 satellites will soon work with some compatible smartphones in the U.S. for additional accuracy.

Most people don't realize that in order for global positioning to work, Einstein's theories of special relativity and general relativity must come into play. On a basic level, GPS finds your position by looking at the time stamp from a number of satellites orbiting the earth, how far away each one is from you, and how far apart each one is from the other. With that data, the system triangulates your position on the ground. But because of relativity, the clocks in the satellites advance ever so slightly faster than clocks on the surface of the Earth. Plus, moving clocks are slower than ones standing still—again, by a very tiny amount.

While those two effects work against each other, the net result isn't equal: You end up with a discrepancy of roughly 38 microseconds per day. That incredibly small difference is still enough to report your actual position off by miles, which would render the GPS system worthless, were it not for allowing for relativistic effects.

The Road to In-Car NavigationEven after 2000, it would be a while before consumers would see GPS navigation in cars en masse. Fortunately, the dot com boom was already coming to the rescue. Beginning around the turn of the century, computer-generated, turn-by-turn directions from websites like MapQuest were a common sight. Not only were these websites godsends for finding unfamiliar hotels and restaurants, but they also assisted plenty of small businesses heavily reliant on driving—think of home improvement contractors, real estate agents, and freight services, just to name a few examples.

Map-based websites weren't perfect, though. Early routing algorithms were imprecise, and sometimes repeated steps over and over again—long lists of instructions that basically said to stay on the same road for 12 miles were a constant source of frustration. Plus, you still had to print them out and take them with you, which meant you needed to pull over to read the next few steps. And if you wandered off course, you were just as lost as you would have been with a map—worse, actually, if you left the actual map at home, since the printed directions were for one specific route.

About the Author

Jamie Lendino is the Editor-in-Chief of ExtremeTech.com, and has written for PCMag.com and the print magazine since 2005. Recently, Jamie ran the consumer electronics and mobile teams at PCMag, and before that, he was the Editor-in-Chief of Smart Device Central, PCMag's dedicated smartphone site, for its entire three-year run from 2006 to 2009. Pri... See Full Bio

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